No, Winter hadn't make a freak return to Bath, in fact I was 90m underground and the “frost” on the floor was mineral salts leaching through the ground… and the treacherous conditions were due to the fact that I was walking along the disused rail bed of a tunnel that has been shut for 42 years in the pitch black.

In a couple of years time though I'll be able to ride through here, no trouble at all – sequential lighting triggered by motion sensors will turn lights on ahead of me and off behind. If I'm heading out of Bath I'll emerge in a deep cutting that will open out slightly and then take me across a viaduct and out through some stunning scenery towards the village of Wellow and on along National Cycle Network Route 24 to the towns of Radstock and beyond that Frome. If I don't fancy that I can hang left just after the viaduct and head off to the Kennet and Avon canal and back to Bath or on to that London… eventually..

It sounds great, the route in question is the Two Tunnels project which aims to link the centre of Bath with National Cycle Network route 24 two and a half miles to the south of the city using an old railway line. This means reinstating bridges removed when the line was decommissioned, renovating a viaduct and, crucially, re-opening the two tunnels that got the railway out of hilly Bath on a relatively level gradient by the simple means of digging through the hills.

Turning all this into a cycle route is going to cost £1.8m, but given the amount of work involved that seems relatively cheap – Bristol, just down the road, with its Cycling City millions has so far struggled to come up with any equally imaginative schemes.

And the Two Tunnels project has captured the imagination of people in Bath, (and far beyond), so far they've raised a fair chunk of the money to pay for it – with initiatives including a massive public arts project that saw variously decorated pigs placed all over Bath last summer and then acutioned off – which raised £200,000. Even some of the most vociferous anti-cyclists on the local paper's website are in favour.

The majority of the money is coming from Sustrans Connect2 – this was one of the flagship projects that helped Sustrans win the Connect2 money in a national poll in 2007. After some foot dragging even the councils is stumping up some cash.

Open days like last Saturday are all part of keeping all that good will going, because making it all happen is going to cause disruption and upset and not everyone is in favour… including some of those who already use the old railway now, and there are probably more of them than the organisers of the Two Tunnels project care to admit. This isn't going to be a great place for dog walking if it attracts the levels of cycle traffic predicted, a situation made worse by local landowners suddenly fencing off adjacent fields and footpaths – the project gets the blame for that too.

The end of one tunnel is filled in at but the other, longer one – is clear, and on Saturday it was open. A fact I'd naturally forgotten. Luckily it's where I walk my dog and we were both alerted to the fact that something was up by the large crowd of people up ahead wearing hard hads and carrying torches… so I nipped home grabbed my camera, and a bike and was back for the last walk through of the day.

So what was it like? Dark and interesting, and surprisingly level. The crowd was made up of interested locals, cycling enthusiasts, railways enthusiasts, and tunnel enthusiasts. I walked through with a Two Tunnels volunteer who remembered the line as a bare cutting in the early Seventies when he was growing up in the area – it's now in a wood. He had driven from Winchester for the day to guide people through. I'm guessing he was a railway man from the joy expressed at finding some track nuts on the floor, but he was also able to point out other points of interest including the slots in the brickwork used to build the wooden scaffolding which I presume acted as both a brace and a platform as the men dug down from the roof.

I missed the 'cathedral' about mid-way along where the roof rises unexpectedly out of sight (well it was dark) probably due to the builders encountering a vertical fissure in the rock in other places they had to brick up horizontal fissures and tunnel through solid rock. Check out the Two Tunnels gallery for more pics and captionsl

At the other end were a couple of pleasant surprises in the shape of a decorated pig, and a very, very lovely bike, a Viking belonging to Frank Tompson, Chair of the Two Tunnels Group just like the tunnel I'd just walked through they don't make 'em like that any more either.